A sheet-shaped prepreg, wherein a molten matrix resin is impregnated into reinforcing fibers arranged in a sheet-like form and the resin is maintained at a semi-cured condition, is utilized broadly in various fields for reinforcing a component, forming a surface, etc. Further, to obtain excellent reinforcement advantage, etc., continuous fibers are frequently used as reinforcing fibers, and in particular, a prepreg, in which continuous reinforcing fibers are arranged in a tape-shaped form, for example, in one direction, and a resin is impregnated thereinto, is preferably employed (for example, JP_A—60-36136).
When such a sheet-shaped prepreg is prepared by a molten resin impregnation process, if a resin which has a high melt viscosity such as a thermoplastic resin is employed as the matrix resin, there is a case that is difficult to impregnate the molten resin satisfactorily all over through the cross section of the tape-shaped reinforcing fiber bundle formed by arranging the continuous reinforcing fibers. Especially, when the thickness of the tape-shaped reinforcing fiber bundle is greater than a certain level, a predetermined impregnation becomes difficult, and a good-quality impregnation form (prepreg sheet) cannot be obtained.
In the case where a material prepared by not continuous reinforcing fibers but, for example, by compounding short fibers of reinforcing fibers randomly in a resin, is employed, although it is possible to form a sheet-shaped base material with reinforcing fibers and resin distributed uniformly by kneading and compounding, etc., in such a manner, a high strength of a molded product and a reinforcing effect such as those achieved in case using continuous reinforcing fibers cannot be expected.
In the case where a molten resin is impregnated into ravings (each having a circular or elliptical cross section) comprising long fibers for reinforcing fibers, it is known that the molten resin impregnating ability into portions between long fibers is improved by spreading each raving (for example, JP-A-2005-29912), and that the molten resin impregnating ability into portions between long fibers is improved by sucking air between long fibers forming the roving (for example, JP-A-5-116142). In JP '142, the rovings are drawn into a die after dividing them one by one. This technology, however, in the case of a tape-shaped reinforcing bundle of continuous reinforcing fibers, when the thickness becomes greater than a certain level, because the resin impregnating ability mainly depends on the viscosity of the molten resin, a high impregnation ability improvement effect cannot be expected. Further, with respect to the resin impregnation time affecting the productivity, for the roving having a circular or elliptical cross section, because the resin impregnation time is regulated by a time for the resin to impregnate from all directions, it is not necessary to improve the impregnation ability in a specified direction, and it is considered that the above-described air suction from the inside of the roving contributes to improve impregnation ability. However, in the case of a tape-shaped reinforcing fiber bundle wherein the thickness is much smaller than the width, because the completion time for the resin impregnation is regulated by the time for resin impregnation in the thickness direction, to attempt to shorten the resin impregnation time, thereby improving the productivity, not only simply performing the spreading fibers, but also a special device to improve the resin impregnation ability in the thickness direction are required.
Except the above-described technologies, in the case where a plurality of roving arranged in parallel are impregnated, it is known that rovings adjacent to each other are alternately divided into separate groups so as not to prevent fiber spreading and particle-like resin is given to them (for example, JP-A-040341). In that technology, however, the rovings are in a condition of being divided into groups when the particle-like resin is supplied into the ravings, and when resin impregnation is actually performed, they are handled as an integral sheet and not divided into groups. Therefore, this technology does not satisfactorily shorten the resin impregnation time in the thickness direction.
Furthermore, to control the cross-sectional shape and gain a flat plane of an obtained sheet-shaped prepreg, it is known to use a pair of vertically arranged convexo-concave rolls (calendar rolls) (for example, JP-A-2000-355629). In that technology, however, only widening by convexo-concave rolls is disclosed, and a necessary factor for the strict control of the constant sheet width, with respect to narrowing after widening in width, is not disclosed at all, and therefore, it is not a satisfactory technical content.
Accordingly, in view of the above-described circumstances, it could be helpful to produce a high-grade sheet-shaped prepreg at a high productivity.